Pharmacokinetic comparison of a combination tablet of enalapril and hydrochlorothiazide with enalapril and hydrochlorothiazide tablets administered together and separately

Lack of effect of colesevelam HCl on the single-dose pharmacokinetics of aspirin, atenolol, enalapril, phenytoin, rosiglitazone, and sitagliptin

AIMS

Drug interactions with bile acid sequestrants are primarily due to the potential of these agents to bind to concomitant drugs. Six clinical studies were performed to determine the effects of colesevelam on the pharmacokinetics of aspirin, atenolol, enalapril, phenytoin, rosiglitazone, and sitagliptin.

METHODS

All six studies enrolled healthy subjects aged 18-45 years. The phenytoin study used a single-dose, three-period crossover design (phenytoin alone, phenytoin simultaneously with colesevelam, and phenytoin 4h before colesevelam). The other studies used a two-period crossover design (test drug alone and test drug simultaneously with colesevelam). Colesevelam (3750mg once daily) was dosed throughout the pharmacokinetic sampling period. After each single dose of the test drug, serial blood samples were collected for determination of plasma drug concentrations and calculation of pharmacokinetic parameters.

RESULTS

For all six test drugs, 90% CIs for geometric least-squares mean ratios of AUC and Cmax for the measured analytes were within specified limits, indicating no interaction between the test drug and colesevelam.

CONCLUSIONS

Aspirin, atenolol, enalapril, rosiglitazone, and sitagliptin may be taken with colesevelam. Although the phenytoin study indicated no pharmacokinetic interaction, phenytoin should continue to be taken ≥4h before colesevelam in accordance with current prescribing information.

Hydrochlorothiazide versus chlorthalidone: evidence supporting their interchangeability

Thiazide diuretics are one of the preferred pharmacologic treatments for hypertension. Hydrochlorothiazide and chlorthalidone have been the 2 most commonly used diuretics in major clinical trials. Treatment guidelines and compendia often consider these 2 drugs interchangeable agents within the class of thiazide or thiazide-like diuretics. Many sources list them as equipotent. Despite these beliefs, there is some suggestion that cardiovascular outcomes are not necessarily the same with these 2 drugs. We conducted a literature search from 1960 to 2003 to identify studies that evaluated the pharmacokinetic and blood pressure-lowering effects of these 2 agents. There are significant pharmacokinetic and pharmacodynamic differences between these diuretics. Chlorthalidone is approximately 1.5 to 2.0 times as potent as hydrochlorothiazide, and the former has a much longer duration of action. Whether these pharmacokinetic and pharmacodynamic features cause differences in outcomes is not known.

Comparison of the pharmacokinetics and pharmacodynamics of perindopril, cilazapril and enalapril

1. The pharmacokinetic and pharmacodynamic responses to enalapril, perindopril and cilazapril have been studied in essential hypertensives (2, 4 and 8 mg perindopril and 2.5 mg cilazapril, single dose and steady state) and normotensive volunteers (10 mg enalapril, single dose). 2. Plasma levels of the active diacid compounds reached similar peaks after single dose administration of the drugs. However, perindoprilat levels persisted for 5 days whereas cilazaprilat levels were not detectable beyond 12 h. 3. The higher levels of perindoprilat were associated with a greater inhibition of plasma angiotensin-converting enzyme (ACE) activity in both acute and steady state studies. 4. The potency of the active diacids in inhibiting plasma ACE activity was perindoprilat greater than cilazaprilat greater than enalaprilat. 5. There was a close relationship between plasma concentration, ACE inhibition and blood pressure decrease. Although both cilazapril and perindopril administration reduced blood pressure in hypertensive subjects, only perindopril exerted 24 h blood pressure control at the doses used.